The present invention relates to a tray-positioning device and in particular relates to a tray-positioning device that utilizes the upper sidewalls of a tray for positioning. Having no mold lines or deformations commonly found on the lower sidewalls of a tray, the upper sidewalls possess smoother surfaces. Hence the tray-positioning device in the present invention is capable of providing higher degree of precision for tray positioning.
Having undergone hundreds of processing steps, a semiconductor wafer is divided into a plurality of dies before being tested and packaged for delivery. To facilitate handling and management, dies are contained and carried around in a designated tray.
FIG. 1 shows a perspective view of a tray 1 for containing dies 2. Being square-slab shaped, said tray 1 possesses a total of four stair-contoured sides, each having a lower sidewall 12 and an upper sidewall 14 such that the upper sidewall 14 is situated on the inner side and above the lower sidewall 12. Said tray 1 provides a number of slots 16, each capable of containing a die 2. The step for transferring die 2 to slot 16 is loading.
In order to raise loading speeding and avoid human contact, most semiconductor plant uses robot arm for loading. If tray positioning is not accurate, the robot arm could not place individual dies on individual slots precisely as programmed.
To point out the importance of tray positioning, the loading process in die sorter is illustrated in the following. FIG. 2 shows a perspective view of a prior art die sorter 3, which comprises a die tray 32, a conveyor 34, a push unit 36 and a robot arm 38. Said die tray 32 is designated to hold a number of dies 2, being divided from semiconductor wafers, for loading. Said conveyor 34 provides an input terminal 341, an output terminal 342 and a sorter position 343. By placing an empty tray 1 on conveyor 34 at terminal 341 and having it carried to the sorter position 343 for loading, followed by sending out an full stray 1 at output terminal 342 after said empty tray 1 is filled with dies. Said conveyor 34 can deliver one or a plurality of trays 1, depending on the programmed loading operation. Prior art die sorter 3 as disclosed in FIG. 2 is useful for delivering a first tray 1 and a second tray 1a. 
Being L-shaped, said push unit 36 includes a pivot 361 and a push rod 362, wherein said pivot 361 is located on one side of the conveyor 34 and said push rod 362 is situated above the conveyor 34 and at an angle with respect to the horizontal position. Knowing that the conveyor 34 can only deliver the first tray 1 and the second tray 1a to the ballpark sorter position 343, pivot 361 will cause the push rod 362 to turn to a horizontal position and drive push rod 362 so as to push the second tray 1a, located behind the first tray 1, and the first tray 1 to the ballpark sorter position 343, simultaneously.
Said robot arm 38 is capable of loading dies by picking up die 2 from die tray 32 and placing it onto slot 16 until all slots of the first tray 1 and the second tray 1a are filled with dies 2.
Being a plastic material, the first tray 1""s lower sidewall 12 often includes mold lines with rough surface. Being the outer rim of tray 1, the lower sidewall 12 is prone to deformation caused by collision or heat. Using the lower sidewall 12, which lacks the smooth surface, for positioning, the prior art tray 1 is incapable of being positioned accurately at the exact sorter position 343, hence preventing the robot arm from loading individual dies precisely and causing production losses.
Aimed at resolving the above disadvantage, the main object of the present invention is to provide a tray-positioning device capable of utilizing the smoother upper sidewall, which has no mold lines or deformations commonly found on the lower sidewalls of a tray, for precision positioning.
The following Description and Designation of Drawings are provided in order to help understand the features and content of the present invention.